Ozone (O3) is a gas with strong oxidation properties that has been used in many applications including the pool and spa industry as well as treating water in water storage tanks since the early 1900's. Ozone is typically produced by high-intensity ultraviolet (UV) light or by a high-voltage electric field. The normal byproduct of ozone is oxygen (O2). Ozone is created when either UV light or a corona discharge (CD) is applied to oxygen. The oxygen disassociates into single oxygen atoms which recombine into ozone. Ozone has a half life of about 2 to 12 hours in air and about 20 minutes when dissolved in water. Ozone is 13 times more soluble in water than oxygen. Ozone oxidizes and disinfects and deodorizes. Ozone also micro-flocculates iron and manganese and kills bacteria 3,000 times faster than chlorine, kills viruses, algae spores, and some parasites, precipitates heavy metals, controls formation of scales, and oxidizes oils.
Ozone is typically introduced into water to be treated by simply bubbling ozone and air into a tank of water with the use of a diffuser stone (known as an ozone aeration system) or by a venturi eductor used in conjunction with a water pump. Passing water through a venturi eductor creates a suction which draws in ozone and mixes the ozone gas with water. The ozone gas is typically introduced into a contact tank from which undissolved ozone gas is vented, or it is introduced directly into a storage tank and bubbles up through the tank and out the top of the tank. This same type of system has been used to inject ozone into water in swimming pools and spas. In some cases, spa systems have used existing “spa hydrotherapy jets” as the means to “suck in” the ozone gas and mix the gas with the spa water.
Ozone is used in combination with various chemicals in the pool and spa industry. Ozone is also used to treat iron, manganese, and hydrogen sulfide in well water and to kill pathogens in, surface waters such as lakes and streams. Ozone systems come in many varieties and ozone is produced in many ways known in the art.
Ozone water treatment systems for water storage tanks are designed to clean “raw” water, e.g., well water, whereas systems for pools and spas are designed to keep treated water clean as it is used over and over again. Prior art ozone aeration systems typically include a filter to remove impurities in a reservoir of water. One prior art system teaches a water purification apparatus suspended inside a water tank. The apparatus includes a filter for filtering the water and a lift tube containing ozonated air bubbles to add ozone to the water in the tank. Such a prior art system is disclosed in U.S. Pat. No. 5,190,648 to Ramsauer, issued Mar. 2, 1993. In the Ramsauer type of system, an ultraviolet (UV) ozone generator utilizes UV light at a nanometer wavelength of 185 that shines on feed gas (air or concentrated oxygen) flowing through a suitable tube chamber. The ozone is injected into the water in an airstream and the airstream causes the water to flow upwardly in the lift tube and circulate from the reservoir through the lift tube for purification. Fundamentally, UV generator mimics the natural process responsible for the production of the ozone layer in the earth's outer atmosphere. In the stratosphere, high-energy UV radiation from the sun splits diatomic oxygen that results in ozone formation. Ozone generators based on UV radiation typically produce relatively small amounts of ozone at a very low concentration.
In the Ramsauer system, air containing ozone generated by an ozone generator is injected into the bottom of the lift tube using a diffuser, which causes the ozonated air to be converted into bubbles. The ozonated air bubbles up through the water in the lift tube and into the water tank. Excess ozonated air escapes through the top of the tank. As taught in Ramsauer, the lift tube is part of an in-the-tank filter module. The ozone gas mixing and filtration and circulation of the water are accomplished within the filter module assembly. The action of the bubbles rising and expanding in the lift tube causes a current flow, which causes the water to be drawn through the filter where the water is filtered with each pass to thereby filter the water prior to its contact with the ozonated air.
Prior art ozone water treatment systems are generally simple to install since they are positioned inside the fluid reservoir and therefore require no cutting into the wall of reservoir, whether it be a pool, spa, or tank, to install separate lines. However, such a “single” reservoir fluid treatment system is more difficult to maintain, because the filter needs to be pulled from the reservoir for cleaning and maintenance. In addition, the Ramsauer system, for example, does not treat the excess ozonated air bubbles emanating from the fluid in the reservoir after treatment, for destruction or to channel it elsewhere for some other use. There is no mechanism for preventing the pool or spa user from being exposed to this ozonated air bubbling off the surface of the water, and thus having to suffer the damaging effects of ozone on the user's mucus membranes, eyes, and skin.
In the prior art, an alternative method for treating water to remove pathogens is to use UV germicidal lamps in disinfection water treatment systems. In such systems, the UV lamp is placed in a flow of water to expose pathogens to UV radiation. These lamps use a different frequency of the electro-magnetic spectrum than is used with UV ozone producing lamps. The optimum wavelength to effectively inactivate microorganisms, according to the prior art, is in the range of 250 to 270 nm. The intensity of the radiation emitted by the lamp dissipates as the distance from the lamp increases.
According to Wikipedia, “UV light is electromagnetic radiation with wavelengths shorter than visible light. UV can be separated into various ranges, with short-wavelength UV (UVC) considered ‘germicidal UV.’ At certain wavelengths, UV is mutagenic to bacteria, viruses and other microorganisms. Particularly at wavelengths around 250 nm-260 nm, UV breaks molecular bonds within micro-organismal DNA, producing thymine dimers that can kill or disable the organisms.” See, https://en.wikipedia.org/wiki/Ultraviolet_germicidal_irradiation.
Many companies offer UV disinfection system for the pool and spa industry. For example, a company called Spectra Light UV sells UV germicidal systems for pools. It states on its website: “Ultraviolet (UV) pool sanitizers utilize a cutting-edge, non-chemical process that uses germicidal UV light rays to sanitize water, air and surfaces that may be contaminated. UV pool sanitizers emit a high intensity germicidal light ray that alters or disrupts the DNA or RNA of targeted organisms such as algae, bacteria, viruses, cysts and protozoa. The highly concentrated electromagnetic energy also destroys organic matter, eliminating the formation of dangerous chlorine by-products. The UV light spectrum was discovered with the identification of light waves. Scientists have known for almost a century that UV is a powerful neutralizer of algae, bacteria and viruses. They also discovered that the optimal ultraviolet wavelength to destroy microorganisms was between 250 and 270 nm. The results led scientists to incorporate UV sanitizer technology into sterilizing drinking water more than 30 years ago. Ultraviolet disinfection has since gained in popularity in drinking water and wastewater disinfection in the last 10 years. Now UV sanitizers disinfect a significant percentage of all drinking and wastewater. Typical germicidal UV sanitizers bombard the passing water flow with a high intensity germicidal ultraviolet ray that destroys more than 60 waterborne pathogens, including algae, bacteria, cysts, and viruses. The UV sanitizing lamp is housed in an industrial graphite housing optimized for high flow rates. A highly specialized quartz glass sleeve protects the lamp from passing water while transmitting 99.9% of the UV light. The highly concentrated electromagnetic energy destroys organic matter and eliminates the formation of dangerous chlorine by-products called chloramines that commonly lead to red, stinging eyes, skin irritations, asthma and allergies. This energy penetrates the cell walls of bacteria, viruses, algae, cysts and all pathogens.” See, http://www.spectralightuv.com/how-uv-works.
Using a system to inject ozone into the water and then, downstream, using a UV germicidal UV lamp for water purification is known in the art. This type of system has many advantages and data shows that the advantages are greater than what might be expected. This is because the use of injecting ozone into the water first and then shining UV radiation makes advanced oxidation products (AOPs). AOPs can achieve greater water treatment results than either ozone or UV disinfection alone. As stated in one prior art publication, Ultraviolet (UV) and ozone are clearly established as viable secondary disinfection methods to chlorine for combating recreational waterborne illnesses (RWIs). As recommended by the Centers for Disease Control and Prevention (CDC) in its recently issued Model Aquatic Health Code, UV and ozone help inactivate Cryptosporidium, the primary causal agent of RWIs, chlorine, unfortunately, is not effective against Cryptosporidium—it is not the end-all, be-all sanitizer, but neither is UV or ozone, which is why, when they are used as a complement to chlorine, greater microbial efficacy is achieved. Microbial inactivation studies employing a combination of UV and ozone have been reported for decades in water treatment. These studies have been made almost exclusively in non-swimming pool applications, so less notice may have been taken of them within the pool and spa industry. In these research investigations, which span multiple water treatment applications, researchers observed a synergistic effect when UV and ozone were used in combination for disinfection and oxidation purposes. That is to say, the observed results were greater than the expected contributions of their parts. The synergistic action, as observed by many investigators, has been attributed to the formation of hydroxyl radicals when UV light interacts with ozone. The use of hydroxyl radicals in water treatment is commonly referred to in scientific literature as advanced oxidation. The potent nature of hydroxyl radicals results in what is effectively a one-two-three punch when UV and ozone are used together.
See, e.g., a study published in 2006 by Magbanua, et al. According to Magbanua, et al., the synergy associated with UV/ozone water treatment is attributed to the presence of supplementary hydroxyl radicals. In pure water, ozone reacts with hydroxide ions to form hydroxyl ions via a complicated pathway. The combined use of UV and ozone promotes the formation of additional hydroxyl radicals by photolysis of ozone through a hydrogen peroxide pathway.
As found in Magbanua, et al., aqueous ozone absorbs UV radiation at wavelengths of 200 to 310 nm, and, in turn, decomposes to form hydrogen peroxide. Hydrogen peroxide then further reacts with UV to produce hydroxyl radicals. Hydroxyl radicals are extremely fast-reacting, potent, non-selective chemical species. In fact, their oxidation power is recognized as being far more potent than chlorine gas, hypochlorous acid or ozone. Furthermore, the reactivity of hydroxyl radicals has long been recognized as extremely fast—in some instances as much as 1 million times faster-acting than ozone for bond breaking via chemical oxidation. For these reasons, the inactivation rate of waterborne pathogens is much greater due to the additional oxidizing power provided by the supplemental hydroxyl radicals.
The trio of UV, ozone, and, hydroxyl radicals (“the trio”) have been found to be effective for water treatment. This dual technology approach, commonly referred to as advanced oxidation, has the capability of achieving oxidation and disinfection. In addition to the research by Magbanua, et al., the combined effects of UV, ozone, and hydroxyl radicals as disinfectants were demonstrated in work performed at the University of Arizona's Water Quality Center under a grant sponsored by the U.S. Department of Homeland Security. In that research, the disinfection performance of UV and ozone against adenovirus and Naegleria fowleri was shown to be remarkably improved when paired together. Importantly, this study established the synergistic effect of UV and ozone against viruses and amoebas, augmenting prior results against bacteria and parasites. Taken together, the potency of a UV/ozone combination as a disinfection approach seems unparalleled.
The trio as Oxidizers: The benefits of pairing UV with ozone do not stop with disinfection performance. While UV has virtually no oxidizing ability, the resulting hydroxyl radicals created from UV and ozone are tremendous oxidizers. As is the case with disinfection, the literature is replete with studies that reflect the superior oxidation performance of hydroxyl radicals formed from UV and ozone. The implications of these findings are significant for swimming pool and spa applications, because urea and chloramines limit chlorine's effectiveness and affect bather comfort. Furthermore, chloramines can volatilize, creating an unpleasant “fishy” or “chlorine” odor, and wreak havoc on indoor materials due to their corrosive nature.
The trio as a Water Treatment Strategy: The synergy that is provided with respect to both oxidation and disinfection is invaluable in most instances. According to the prior art, however, neither UV nor ozone, nor the resulting hydroxyl radicals, provide a lasting disinfection residual. Therefore, in some applications, such as pools and spas, chlorine is still a necessary part of the overall treatment strategy. To this end, the Centers for Disease Control & Prevention (CDC) recommends to use of either UV or ozone as a secondary disinfectant to chlorine for swimming pools and spas. See, http://www.wqpmag.com/power-three.
More recently, the CDC recommends in its Model Aquatic Health Code that the UV and ozone technologies as secondary disinfectants to combat outbreaks of recreational water illnesses in aquatic facilities. As one prior art commentator indicated, the net benefits of the UV/ozone combination are attributed to the formation of hydroxyl radicals, resulting in the “power of three” for increased disinfection and oxidation efficacy.
UV & Ozone Technology Integration: It is certainly possible to install a separate ozone system before or after a UV system to achieve a dual disinfection strategy. To do so, however, requires two separate systems and installations, which can be expensive. Fortunately, some low-pressure UV lamps can emit two wavelengths: 185-nm UV light for the generation of ozone and 254-nm UV light for inactivating microorganisms. These dual-wavelength lamps are available from most UV suppliers, cost about the same as single-wavelength UV lamps and can be engineered into a single system to deliver simultaneous UV and ozone water treatment. Creating a UV/ozone combination system requires a fundamental understanding of how a conventional low-pressure UV system is configured. In such systems, UV lamps are housed in a vessel so that water passing through is exposed to the UV rays. To do this, each lamp (and there may be more than one) is surrounded with a quartz glass sleeve. This sleeve performs two key functions, it provides a physical barrier between the lamp and the water, and it allows the lamp's UV rays to be readily transmitted into the water phase. If the UV lamps used in the vessel are single-wavelength lamps, also known as germicidal lamps (i.e., lamps that emit only in the range of 254-nm UV light), then the system is a conventional UV system.
To convert a conventional system into a combination UV/ozone system requires two key steps: replacing the UV lamp with a dual-wavelength model, and providing a means to remove the ozone created inside the quartz sleeve area and inject it into the water phase. While there are a variety of methods to extract ozone from the sleeve area, the simplest and most common is through the use of a venturi, a favored approach because venturis have no moving parts and can utilize the water flow in the piping to create a suction, or ozone draw. As water passes through the plumbing, the venturi will draw air from the source to which it is connected. If the venturi is connected via tubing to the sleeve area around a lamp, the air it draws will contain ozone, as the UV light produces ozone from air using its 185-nm wavelength. When more than one lamp is used, a simple manifold can combine the air draw from all of the sleeves. The ozonated water that enters the vessel is struck with the 254-nm UV light. It is the 254-nm UV light, not the 185-nm UV light, that is transmitted through the glass sleeve surrounding a lamp. The 254-nm UV light converts the ozone into hydroxyl radicals, creating the one-two-three punch described above. While the quantity and concentration of ozone generated are small, it is known that this can be significant in contributing to the effects of both disinfection and oxidation. The injection of ozone can be done before or after the UV light, but ozone must be injected before the UV vessel to take advantage of hydroxyl radical formation. When performed this way, no residual leaves the vessel, as the half-life of hydroxyl radicals is a fraction of a second. As a result, no ozone degassing or destruction chamber is needed, as is the case when corona discharge ozone systems are used.
A combination ozone/UV germicidal lamp unit connected to and operated with a water pump pool recirculating system is available through a company called Del Ozone. According to Del Ozone, by combining ozone and germicidal UV in a single unit, the “UV light interacts with the ozone, and the resulting chemical reaction generates hydroxyl free radicals. Hydroxyl free radicals have even more oxidation potential than ozone, the power of the whole system is increased; creating the synergy of Advanced Oxidation Process (AOP)”. See: http://www.delozone.com/files/4-1958-01_Rev_C.pdf.